We have aligned the microdomains of a polystyrene-b-poly(2-hydroxyethyl methacrylate)-b-poly(methyl methacrylate) (PS-b-PHEMA-b-PMMA) triblock copolymer during preparation from solution by virtue of an external electric dc field (1.8 kV/mm). Bulk samples cast in the presence of an electric field exhibit lamellar microdomains highly oriented parallel to the electric field vector, as shown by small-angle X-ray scattering and transmission electron microscopy.